The aim is to stimulate the human eye with test fields that are precisely controlled with respect to motion of the retinal image. The zero-motion (stabilized) condition is of particular interest. In this case, a special feedback type of optical system is used to counteract the normal saccades, drift and tremor that take place as the subject attempts to fixate steadily. The result, if stabilization is sufficiently accurate, is that the contours of the test field disappear and visual thresholds rise steeply as stabilized viewing is continued. A steady state of visual impairment is then reached, during which visual capacity can be evaluated by determining spatial and temporal resolution thresholds. A particular feature of the proposed research is that detailed comparisons can be made, using the same human subjects, between earlier techniques based upon fitting the eye with a contact lens and mirror device and a new eye-tracking technique based on the relative positions of the first and fourth Purkinje images.